Exhibit 4.3

     THIRD SUPPLEMENTAL INDENTURE (this “Third Supplemental Indenture”), dated as of June 15, 2011, among International Coal Group, Inc., a Delaware corporation (the “Company”), the Guarantors (as defined in the Indenture referred to herein) and The Bank of New York Mellon Trust Company, N.A., as trustee under the Indenture referred to below (the “Trustee”).

W I T N E S S E T H

     WHEREAS, the Company has heretofore executed and delivered to the Trustee an Indenture, dated as of March 16, 2010 (the “Original Indenture”), as amended and supplemented by the First Supplemental Indenture, dated as of March 16, 2010 (the “First Supplemental Indenture” and, together with the Original Indenture, the “Indenture”), providing for the issuance of 4.00% Convertible Senior Notes due 2017 (the “Securities”);

     WHEREAS, the Company is a party to an Agreement and Plan of Merger, dated as of May 2, 2011 (as amended and supplemented from time to time, the “Merger Agreement”), by and among Arch Coal, Inc., a Delaware corporation (“Arch”), Atlas Acquisition Corp., a Delaware corporation and wholly owned subsidiary of Arch (the “Purchaser”), and the Company, pursuant to which the Purchaser merged with and into the Company (the “Merger”), with the Company surviving the Merger and becoming a direct wholly owned subsidiary of Arch;

     WHEREAS, the Merger became effective at 12:01 a.m., Eastern time, on June 15, 2011 (the “Effective Time”) and, from and after the Effective Time, each share of Common Stock issued and outstanding immediately prior to the Effective Time (other than Common Stock owned by the Company, Arch, the Purchaser (prior to the Merger) or any of their respective subsidiaries and Common Stock held by dissenting holders of Common Stock who properly exercise appraisal rights under Delaware law), by virtue of the Merger and without any action on the part of the holders of the Common Stock, was cancelled in exchange for the right to receive $14.60 per share, net to the seller in cash, without interest and subject to any withholding taxes (the “Merger Consideration”);

     WHEREAS, Section 9.12 of the First Supplemental Indenture provides that in connection with the Merger the Company shall execute with the Trustee a supplemental indenture providing that, at and after the effective time of the Merger, any shares of Common Stock that the Company would have been required to deliver upon conversion of the Securities in accordance with Section 9.02 of the First Supplemental Indenture shall instead be deliverable in the amount and type of consideration that a holder of that number of shares of Common Stock would have received in the Merger;

     WHEREAS, Section 8.01(ii) of the First Supplemental Indenture provides that the Company may amend or supplement the Indenture without notice to or the consent of any Securityholder to make provisions with respect to adjustments to the Conversion Rate in accordance with the First Supplemental Indenture;

     WHEREAS, the Company has heretofore delivered or is delivering contemporaneously herewith to the Trustee (i) copies of resolutions of the Board of Directors of the Company

authorizing the execution of this Third Supplemental Indenture and (ii) the Officers’ Certificate and the Opinion of Counsel described in Section 9.06 of the Original Indenture; and

     WHEREAS, all other acts and proceedings required by law and the Indenture necessary to authorize the execution and delivery of this Third Supplemental Indenture and to make this Third Supplemental Indenture a valid and binding agreement for the purposes expressed herein, in accordance with its terms, have been complied with or have been duly done or performed.

     NOW, THEREFORE, in consideration of the foregoing and notwithstanding any provision of the Indenture which, absent this Third Supplemental Indenture, might operate to limit such action, the parties hereto, intending to be legally bound hereby, agree as follows:

ARTICLE I

AMENDMENTS

     1. Settlement Upon Conversion. Subject to and upon compliance with all the provisions of the Indenture, upon conversion by a Holder of each Security then outstanding, the Holder shall have the right to receive the Merger Consideration for each share of Common Stock into which the Holder is entitled to convert such Security (after giving effect, if applicable, to any additional shares of Common Stock that such Holder would have been entitled to receive if it converts its Securities during a Make-Whole Conversion Period), and upon conversion of the Security by a Holder, the Company shall pay to such Holder cash in an amount equal to the amount such Holder would have received as Merger Consideration had such Holder converted its Securities at the Conversion Rate in effect immediately prior to the Merger (after giving effect, if applicable, to any additional shares of Common Stock that such Holder would have been entitled to receive if it converts its Securities during a Make-Whole Conversion Period).

     2. Effectiveness. This Third Supplemental Indenture will become effective and operative and binding upon each of the Company, the Trustee and the holders of the Securities as of the Effective Time.

ARTICLE II

MISCELLANEOUS

     1. Capitalized Terms. Capitalized terms used herein without definition shall have the meanings assigned to them in the Indenture.

     2. New York Law to Govern. The internal law of the State of New York shall govern and be used to construe this Third Supplemental Indenture without giving effect to applicable principles of conflicts of law to the extent that the application of the laws of another jurisdiction would be required thereby.

     3. Counterparts. The parties may sign any number of copies of this Third Supplemental Indenture. Each signed copy shall be an original, but all of them together represent the same agreement.

     4. Separability. In case any provision in this Indenture or in the Securities shall be invalid, illegal or unenforceable, the validity, legality and enforceability of the remaining provisions shall not in any way be affected or impaired thereby and a Holder shall have no claim therefor against any party hereto.

     5. Effect of Headings. The Article and Section headings herein are for convenience only and shall not affect the construction hereof.

     6. Trustee’s Acceptance. The Trustee accepts the modifications of the Indenture effected by this Third Supplemental Indenture, but only upon the terms and conditions set forth in the Indenture. Without limiting the generality of the foregoing, the Trustee does not assume any responsibility for the correctness of the recitals herein contained, which shall be taken as the statements of the Company and the Guarantors. The Trustee makes no representation or warranty and shall not have any responsibility as to the validity or sufficiency of this Third Supplemental Indenture or the proper authorization or the due execution hereof by the Company or the Guarantors.

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     IN WITNESS WHEREOF, the parties hereto have caused this Third Supplemental Indenture to be duly executed and attested, all as of the date first above written.

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